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  1. #1

    Disable Carrier vapor pressure switch?

    I have a Carrier 410A heat pump that's about 10 years old. Last week, I noticed that that condenser fan was cycling on and off every three-to-five minutes, while the condenser continued to run. I don't think it was going into defrost mode, because I could see frost forming on the unit while the fan was off, then melting away after the fan went back on. The unit also started making an intermittent clunking sound I'd never heard before - three metallic clunks every few minutes.

    Our contractor diagnosed a bad defrost board and replaced it. The clunking stopped, but the fan continued to cycle on and off, though not as frequently. With the new board installed, the fan repeatedly would run five-to-ten minutes, then turn off for about 90 seconds. (Outdoor temperature was about 40 degrees.)

    This time, the contractor said the issue was the "Pressure Guard" vapor pressure switch. He bypassed the switch, and that eliminated the issue of the cycling fan.

    In doing some reading on Carrier's website, the company says Pressure Guard was included on 410A heat pumps 10-15 years ago to comply with burst requirements in regulatory codes that were written for R22. (Though the contractor thought the switch was bad, I'm thinking it probably was functioning properly on our unit, cycling the fan off in regular intervals to reduce pressure in moderate weather.) By 2003, the codes had been revised and Carrier eliminated the switch, which it had concluded was unnecessary.

    Carrier's site doesn't address whether it's okay to bypass the switch on older units, but our contractor said his company does so routinely to increase efficiency and prevent problems from malfunctioning switches. Does anybody have any thoughts/experience with this?

    Thank you.

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,745
    Lower end eqipment doesn't have any kind of safeties like you mention. While they are good to protect the equipment they are not necessary so it shouldn't be a problem. Never seen a factory safety like you mention though, sounds like a freeze protection device (freeze stat) which is usually an aftermarket item for systems used in air conditioning with low outdoor temperatures. Correct me if I'm wrong in my assumption.

  3. #3
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,861
    yes carrier did have the vapor pressure switch on the early 410 systems to keep the head pressure down in heat mode . in reality the real problem as to why the pressure is getting to high needs to be addressed .
    We really need change now

  4. #4
    The switch was original equipment on the unit. There's a description of it on page 13 of the manual:

    http://www.docs.hvacpartners.com/idc...it/38-12sm.pdf

    Here's the service bulletin when Carrier decided to stop including it on new units in 2003:

    ftp://ftp.mingledorffs.com/Tech_Serv...at%20Pumps.pdf

    Correct me if I'm wrong, but it looks like the vapor pressure switch is designed to open and stop the fan even if there's not high pressure. The specs show a cut-out pressure around 400, so I'm thinking that frequent fan interruptions would be normal on a 40+ degree day, right? Carrier says in the service bulletin that they were only manufacturer to use the switch, so I'm hoping that means it's not necessary.

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,586
    Actually Nordyne is going to start suggesting them! They are going to microchannel indoor coils which hold little refrigerant. They were having issues of high head pressure on mild days, usually over 50 some out so they are suggesting we add them to keep the pressures down on mild days. Go figure.

  6. #6
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,745
    Quote Originally Posted by BaldLoonie View Post
    Actually Nordyne is going to start suggesting them! They are going to microchannel indoor coils which hold little refrigerant. They were having issues of high head pressure on mild days, usually over 50 some out so they are suggesting we add them to keep the pressures down on mild days. Go figure.
    Microchannels are cool but seems to be more problematic than the smaller footprint is worth IMO especially for heat pumps it just doesn't seem like a good idea. How does nordyne make the mc evap drain properly in cooling? Seems like it would have to have a pan under the whole coil restricting air flow and the coil itself would clog up easily bc of tight packing of tubes. I know the York mc outdoor units need to be rinsed off every couple years bc they get clogged easily.

  7. #7
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,861
    Quote Originally Posted by BaldLoonie View Post
    Actually Nordyne is going to start suggesting them! They are going to microchannel indoor coils which hold little refrigerant. They were having issues of high head pressure on mild days, usually over 50 some out so they are suggesting we add them to keep the pressures down on mild days. Go figure.
    is this also for r22 units
    We really need change now

  8. #8
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,586
    The Nordyne systems with MC inside are all 410. The coils look like any other A coil. They say they put a lot of research into draining and we had no complaints all summer.

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